Idiopathic Pulmonary Fibrosis (IPF) is a chronic progressive lung disease. This application will examine the hypothesis that epigenetic dysregulation underpins pulmonary fibrosis. We will examine miRs-19b and -20a, two members of the miR-17~92, which target DNA methyltransferase-1, DNMT1. We found that miRs-19b and -20a expression are reduced in the lung tissue of patients with IPF, accompanied by increased expression of DNMT1. Thus, the grant application investigates the role of DNMT1 in IPF and the relationship of miRs-19b and - 20a in this regulation. Moreover, we believe that the cluster itself is also regulated by DNA methylation of CpG islands in its promoter, forming a negative feedback loop between DNMT1 and miRs-19b and - 20a expression. In this proposal, we will use in vitro and in vivo studies to assess this hypothesis. To address our hypothesis in vivo, we have generated cell-specific miR-17~92 and DNMT1 knockdowns in transgenic murine models. We will also examine whether miRs-19b and -20a regulates components involved in epigenetic regulation. We anticipate that understanding the relationship between miRs-19b and -20a and DNMT1 expression in lung fibrosis will identify novel therapeutic strategies and underlying mechanisms of fibrosis. We predict that our findings will lead to the development of human clinical trials. To accomplish these goals, we propose the following two specific aims: Specific Aim 1) Understand the role of DNMT1 in expression and methylation of the miR-17~92 cluster in vitro and the reciprocal role of miRs-19b and -20a on DNMT1 expression. Specific Aim 2) Determine the in vivo role of DNMT1 in pulmonary fibrosis.